Non-invasive, non-destructible analysis of whole tablets can be carried out by means of near-infrared (NIR) or Raman spectrometry. The common feature of both these techniques is that they utilise light in the NIR wavelength region (700–2500 nm, specifically 700–1500 nm) where pharmaceutical tablets is several millimetres and information on the content can be obtained from the inside of the tablet and not only from the surface. Measurements on a solid dosage form such as a tablet, a pellet or a capsule, are conducted to obtain information for example on the concentration of the active drug and/or the concentration of non-active components or their spatial distribution, i.e. homogeneity. In particular, it is of interest to monitor the quality consistency of doses during the manufacturing process. Thus, real-time measurements during the manufacturing process, for example during the tabletting process, may reveal important information to be used for controlling the process.
Typically, the prior-art tablet analysers acquire a spectrum for each tablet being analysed during an analysing time period when the sample is positioned in the measuring or analysing light beam. To this end, optical tablet analysers conventionally comprise some sort of tablet positioning unit for presentation of one tablet at a time to the analysing beam(s). Firstly, the prior art includes single-tablet positioning units; i.e. positioning units that can support only one tablet at a time, namely the tablet being analysed. Secondly, the prior art includes multiple-tablet positioning units arranged to hold multiple tablets at a time for performing multiple spectrometric measurements by sequentially presenting the tablets to the analysing beam(s).
EP 0767 369 A discloses an apparatus for NIR transmission measurements of tablets containing pharmaceutical compounds. An object of this apparatus is to minimise or eliminate the incidence of stray light reaching the detector and therefore, a sample locator is used together with a masking device. The sample, a tablet, is positioned in a cylindrical well within the locator and thereafter an annular masking element is placed within the well to engage the top surface of the tablet. In this way the possibility that light will leak around the sample is minimised. One embodiment comprises a single-tablet holder having only one single-tablet receiving well for performing a single-tablet analysis. Another embodiment comprises a multiple-tablet holder in the form of a rotating plate provided with several tablet-receiving wells spaced circumferentially on the rotating plate for performing a multiple-tablet analysis of a predetermined number of tablets.
The insertion of the tablets into each well has to be done manually prior to the analysis. Therefore, the number of analyses is limited to the number of wells in the sample locator, which precludes its use for continuous automated analysis. A further drawback is that due to different physical parameters of each well, such as tolerances, dimensions, surface finish etc., the wells of a given plate will not be mutually identical. This fact will introduce imprecision in the analysis.
DE 4441686 A relates to an apparatus for testing tablets. From a batch source containing tablets to be tested, tablets are transported via a vibrating table down to a sloping table from which the tablets fall onto a rotating testing plate comprising drilled cavities to receive tablets. The tablets are exposed to a light beam from a light source hanging above the testing plate and a detector is placed under the testing plate.
In this prior art device a continuously automated analysis can be performed. However, due to different physical parameters of each cavity, such as tolerances, dimensions, surface finish etc., the cavities will not be identical. This fact will introduce imprecision in the analysis. Further, vibrations from the vibrating table are likely to effect the rotating test plate. These vibrations will disturb the on-going measurements.